text:
What methods are used for calculating maximum takeoff windspeed of a helicopter?
I would like to calculate the maximum windspeed in which a helicopter may safely take off and safely land, assuming a theoretical wind environment with constant wind direction and no gusts.
I understand that Effective Translational Lift is generated when taking off into the wind, which increases the climb rate.
However, I would like to understand at what windspeed taking off and landing into the wind is theoretically no longer possible for a given main rotor RPM.
Some factors I have considered include:

while the main rotor is spinning at less than flight RPM, and nonrigid, that it may come in contact with the fuselage.
during takeoff or landing: if the vehicle must pitch forward to compensate for extremely strong headwinds while inches above the ground, the main rotor may strike the ground

While not relevant to the theoretical wind environment described above: if there are gusts, I have also considered:

during takeoff or landing: while hovering inches above the ground, a strong crosswind may roll the vehicle above a threshold which causes the main rotor to strike the ground.

What methods might I use to calculate these (and any other factors I have not considered) precisely?

You may include what you think are the limiting factors, in particular why you think this differ from flying at high speed.

Is it your intention to fly in a hurricane?  The problem with wind speed limits is (typically) in going from 0 RPM to flight RPM as the engine begins to turn the rotor, before the stiffness of the CF loads are fully realized.  The transitional rotor speeds can lead to some unusual rotor blade behavior during high and / or gusty winds, depending on wind direction. Taking off and landing is less of a problem because you can always point into the wind.  Which leaves me with: what problem are you trying to solve with this question?  We seem to be missing something. The question makes no sense.

For example of what is missing - what is the highest airspeed that your model of helicopter can fly at? (An R-22 has a lower max speed than an S-92, for example)

Thanks @KorvinStarmast - I do not have any particular helicopter in mind (and do not own a helicopter), but would like to understand the math and physics that correlate rotor speed during startup with maximum tolerable winds. I do not intend that any pilot would fly in hurricane force winds. However, if instead the vehicle were automated, I would like to know what helicopters would be theoretically capable of flying in hurricane force winds. Because takeoff wind speed is a greater limiting factor than high winds during flight, I am asking about the theoretical limits of takeoff wind speed.

@ManuH - possibly 1) during takeoff: while the main rotor is spinning at less than flight RPM, and nonrigid, that it may come in contact with the fuselage. 2) during takeoff or landing: if the vehicle must pitch forward to compensate for extremely strong headwinds while inches above the ground, the main rotor may strike the ground 3) during takeoff or landing: while hovering inches above the ground, a strong crosswind may roll the vehicle above a threshold which causes the main rotor to strike the ground. Are you aware of methods for calculating these factors precisely?

@max, you should include those information in the question description.

Max, you don't seem to have done enough research during takeoff: while the main rotor is spinning at less than flight RPM That is not correct. Helicopters go from engines off to flight RPM before they get off the ground.  You get to flight RPM, then you leave the ground.

@KorvinStarmast my apologies, "during takeoff" is superfluous (and incorrect) to the core statement, which could begin with "while the main rotor is spinning at less than flight RPM...". I was referring to the broader takeoff sequence of events, as compared with landing, and do understand the main rotor must reach flight RPM prior to the vehicle departing the ground.

@ManuH I originally did not include my guesses to avoid potentially biasing answers, but have now edited the question description to include them.

@max including your current state of research helps us adapt the answers and if needed help you bring new elements to precise your question.

"during takeoff or landing: if the vehicle must pitch forward to compensate for extremely strong headwinds while inches above the ground, the main rotor may strike the ground" Why would the helicopter have to pitch forward? Usually you would just pitch the blade disc forward and there's no way it could come into contact with the ground (unless you were up against a hill)...

@RonBeyer -- the quote said "while inches above the ground", not while still on the ground.  Is there not a tendency for the fuselage to tilt along with the rotor disk?  See for example concepts in this related answer -- https://aviation.stackexchange.com/a/38904/34686 .  It seems to me that there would indeed be some wind speed above which a helicopter could not hover inches above the ground without the rotor disk striking the ground.

@max I'm guessing that in reality, by the time the wind is strong enough that even if it were 100% steady, take-off would be theoretically impossible for any of the reasons you suggest, any real-world wind would involve so much gustiness that no one in their right mind would even consider taking off or landing.  May not always be true though, for example in stable marine air over cold ocean water, such as might be found at on oil platform landing site.  Just a thought.  Good questions though in my opinion.  Perhaps could be improved by specifying a steady wind completely free of gusts?

Max, have you ever flown a helicopter?  If I were to be Flying directly into a 70 knot head wind I'd be almost level with the ground, pitch attitude wise, in the five helicopter models I can think of off the top of my head.  Landing would be no problem at all.  The harder thing would be trying to do pedal turns or sidewards flight.  Most helicopters I am familiar with would not handle that well or at all.  And then, as we turned off the engines and the rotors slowed down, I'd be looking at my manual and the limitations therein I'd wonder "uh, what happens next?" as I'd be outside of limits.

Thanks @quietflyer - I have updated the question description to include clarify a theoretical wind environment without gusts.

The simple (and probably unsatisfying) answer would be:
The maximum headwind into which a helicopter can land will be somewhat less than it’s listed maximum operating speed.
Flying at Vmo into a headwind of equal speed should lead to a stationary velocity relative to the ground. In theory, the aircraft could gently lower itself all the way the ground like this (although, I certainly wouldn’t try it). The problem is, most helicopters will be in a very pitch-forward attitude at this point and the skids or landing gear may not be in the proper orientation to safely put the aircraft on the ground. This will vary from model to model and would need to be tested on a case-by-case basis.
It should be noted that landing and shutting the engine down are 2 separate problems. Many helis have a maximum wind speed for startup/shutdown, like this BK117 which has a listed limit of 50 knots in its POH.


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Why does the temperature rise in the boundary layer after a shock wave?

Is it because the BL thickens after the shock so the drag increases, causing a increased friction? Here M=0.82 far from the airfoil, the picture represents the static temperature in Kelvins around the symetrical airfoil at angle of attack 0°.

This is the total temperature for a supposedly everywhere adiabatic flow.

This is not the static temperature but the Mach number, for $M_{\infty}=0.70$

Mach number for $M_{\infty}=0.80$

Mach number for $M_{\infty}=0.99$

Mach number for $M_{\infty}=1.20$
I understand that as velocity decreases, temperature rises, but I have another file that shows the evolution of static pressure and it does not increase as static temperature does, after the shock in the BL.
Thank you

What is this picture representing? The scale/color seems odd and counterintuitive, whatever it is. There is no unit given.

Can you get the same picture at Mach 0.3, 0.5, 0.7, 0.9, 1.2.  Huge info here.  Temp rise could be compression or friction.  But striking is the bow shock wave changing the shape of the low pressure areas, allowing encroachment of higher pressure from behind the wing (similar to stalling). This "encroachment" may be forming a "tidal bore" on the curved surface. Is this the "shock wave"?  Also, is the low pressure area saying "this is what my wing wants to look like at Mach 0.82"?

@Jpe61 the first picture is representing the stagnation (static?) temperature around a symetrical airfoil. What would you have set for the color scale? The unit is K. These images have been provided to all students by the teachers because of the current quarantine.

@Robert Digiovanni I edited my post with the pictures of the Mach number for 0.7, 0.8, 0.9 and 1.2 . I will come back with the pictures of the stagnation temp instead of the Mach number as soon as I run the files in Paraview, however I only have the files from 0.7 to 2. Thank you both for your answers! I'll dig deeper with what you gave me :)

@JZYL It is adiabatic. What if it was isothermal?

@JZYL Oh my mistake, I thought stagnation temperature was static temperature, English is not my primary language and I saw the term stagnation in a book. So this is actually the static temperature. I also have the total temperature and at the same location we can observe a small variation (less than 2K) although the teachers told us the flow is adiabatic everywhere. Maybe did I miss something?

Let us continue this discussion in chat.

It is customary to use colour gradient in such a manner that red end of spectrum represents hotter temps, blue colder. Your representation is reversed isn't it.

It is my teacher who has chosen the colour gradient. Your point of view makes more sense, though for instance a blue star is hotter than a red one and the same goes for any heated body if I'm not mistaken. Also, I said before the flow is adiabatic but it isn't : the first image shows an increase in temperature (static and total) after the shock, due to viscous forces

Gotta hand it to your teacher, he/she is quite a trickster. There is no justification to reverse the colours, except for testing the students...

Due to no-slip condition, the flow immediately adjacent to the wall has no velocity relative to the wall. If the flow is adiabatic everywhere and there is no significant viscous stresses (more on that later), then the total enthalpy ($h_0$) is constant; if we assume that the gas is calorically perfect (good assumption for air at low supersonic speeds) and that the heat capacity is constant (good assumption for small temperature variation), then:
$$h_0=c_pT_0=c_pT+\frac{1}{2}V^2$$
where $T$ is the static temperature, $T_0$ is the total temperature, $V$ is flow speed.
Immediately adjacent to the wall, the flow static temperature will increase toward the total temperature (around 315K in your example). This occurs in boundary layer both before the shock and after. The boundary layer before the shock is thin, so you can't really see it when zoomed out. After the shock, the boundary layer is greatly thickened along with an amplification in turbulence, so the effect is much more prominent.
Now let's revisit the part about viscous stresses, which are prevalent in the boundary layer. Viscous deceleration is not exactly adiabatic (Ref. Hill, Mechanics and Thermodynamics of Propulsion), so there is decreased total temperature immediately adjacent to the wall (characterized by the recovery factor), and an increase in total temperature farther away, before tending to the free-stream value.

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How are range violations during a launch countdown handled?
I was watching the ULA Atlas V IBIRS countdown tonight but the launch was scrubbed (after some technical issues) ultimately because of a range violation: an airplane was in the restricted area.
I've seen this happen because of boats before, but I know it also sometimes happens because of wayward planes. Specifically: Is this just a standard airspace violation? Or is it treated differently since this particular launch was military-related? Whose job is it to keep the airspace clear, how do pilots know to stay clear of the area, and what happens to the pilot(s), if anything?
(Here's a more detailed tweet thread that has some interesting discussion.)

I believe they said that there was an aircraft that would have been in the range at T-0 (based on a call I heard after the hold), not that it was actually there. I'm surprised ATC couldn't re-route or something, this caused the launch to scrub for 24 hours...

Depending on the exact type of the rocket, the exact launch sequence, and the exact time the range violation was detected, moving the launch by 24 hours may have been the simplest / safest / cheapest option. After all, in the most extreme case, if you wait too long to see whether ATC can re-route the plane, and it turns out they can't, the only way to scrub the launch is to blow up the rocket! 24 hours is not a long time, and they are prepared for launch delays anyways, for minor technical problems, upper-altitude winds, rain, lightning, etc. If this was a launch that could only happen once a

decade, they probably would have made a different decision.

As far as the FAA is concerned, it's just an airspace violation.  There is a restricted area over the center/base that extends up to 5000 feet.  This is active continuously.  There are other restricted areas that extend up to 'unlimited' that are "Intermittent by NOTAM normally 24 HRS in advance."
So high altitude traffic is not impacted by the continuous restriction and when there is a launch the restriction is published by NOTAM in advance.  This gives ATC the ability to route traffic around the area without any significant impact.  Since the safety area extends out into international airspace, the FAA can't control it as restricted airspace.  They have been defined as FAR 91.143 airspace, which states:

§91.143   Flight limitation in the proximity of space flight
  operations. When a Notice to Airmen (NOTAM) is issued in accordance
  with this section, no person may operate any aircraft of U.S.
  registry, or pilot any aircraft under the authority of an airman
  certificate issued by the Federal Aviation Administration, within
  areas designated in a NOTAM for space flight operation except when
  authorized by ATC.

So violation of the NOTAMed airspace is a violation of 91.143.
In my experience (5 years working launch ops) the issue usually arises with GA aircraft that want to watch.  If someone enters the area, ATC will try to contact them by radio.  There are also helicopters and or plane that can intercept and escort the aircraft clear.  Space Shuttle launches had the largest contingent of aircraft.  Some small booster ops might have one helo or a King Air to deal with intruders.
The aircraft can also be used to get the attention of boats in the area.
Whether you scrub a launch or not depend on the launch window. I've seen them range from a few minutes to several hours.  A violator at the wrong time will cause a scrub with a short window, while you can handle the delay with a larger window.

It kind of depends of how much you are violating.
For Kourou Space center, according to the following sources (french):

First step is a simple radio contact.

No big deal if you can respond, excuse yourself and leave quickly.

Second one is interception by an helicopter.

I remember seeing an emission on youtube where they do that. It involves someone aiming directly at the pilot with an assault rifle
 Source:
http://www.defense.gouv.fr/actualites/dossiers/guyane-le-role-des-militaires-dans-ce-departement-d-outre-mer/guyane/operation-titan-securisation-sol-air

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text:
What happens to the dynamic temperature in the boundary layer at supersonic speed?
In the boundary layer for a supersonic flow, does the dynamic temp decrease?
Thank you

Thank you :) I changed the question

related: How can dynamic and static pressure be explained?

This question shows no research.

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WWII fuel gauge: single needle and dual range
In T-34 movie there is a scene where a WWII small aircraft is flying:

and the pilot warnings the official that they're running out of fuel and a quick close up of the cockpit shows the fuel gauge:

Why it has two sides with (90 as full scale range) with a zero in the middle and a single needle? How is it supposed to work?

I don't know for sure, but I suspect there are separate left and right wing tanks and a switch to determine which is being used.  This could be a clever indicator both of quantity, but also which tank.  Some aircraft allow independent switching of which tank is being used (a valve) and which is being measured (wires).  However, the instrument is usually measuring a resistor in the sending unit by measuring a voltage -- and it wouldn't know left from right...

The Comic Sans tells you all you need to know about the accuracy of the scene.

Did the Fieseler Storch even have a fuel gauge in the panel? Is hard to find a clear answer online, but I'm getting the impression it may have had sight gauges.

The lowercase "k" in kraftstoff gives this away as an unauthentic, made-up instrument. The proper way would be capitalized, as in Kraftstoff.

Odd enough! They used a real airplane for the scene and didn't take a picture of the cockpit, but made up a fake one...

That looks like an animated cockpit, and if i was a betting man Id say that someone googled "german airplane gauges" and didn't know what they are looking at. The labeling on the spectrum is likely from an Amperage gauge similar to this one from the era. They generally display charge/discharge centered on 0. The animator then labeled it "fuel" incorrectly.
Fuel gauges from that era were indeed what you expect in reality.


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Can someone identify this plane?
This aircraft was circling very low during the day, wondering if anyone could identify this plane.
this was spotted flying over the san francisco bay area.

If you feel comfortable doing so, telling us the approximate location and date/time the photo was taken can help ID it.

It’s definitely a C-130.  If you tell us your approximate location, we may be able to pin down the exact variant or even the tail number.

And FWIW, that's not really low, at least for C-130 training flights hereabouts.

@jamesqf You don't know what lens it was taken with. With a wide-angle it could have been at 100ft :-)

i just added location: san francisco bay area

Either Coast Guard or Cal Fire. They operate a LOT of C130's in the area, a lot coming out of Sacramento and flying out over the bay. I doubt it's the KC-130 variant (for aerial refueling), those are likely external fuel tanks for extended range and/or loiter duration.

@DJClayworth it was taken from a phone... the rectangular size tells us that much at least.

@SnakeDoc: I believe they also specifically land at and take off from the Moffet Airfield. I used to live very close to it and there were a lot of them.

@DJClayworth: I'm going by probabilities, e.g. the format & general image quality suggests it was taken from a phone.

@SnakeDoc You'd be able to tell that it was Coast Guard or Cal Fire even with this lighting, because they both employ brightly painted paint schemes.

@mathrick I believe they do take off, landing and go-around practice at Moffet Field

@Davidw sometimes during fire season, we see Air National Guard C130's with a Red Slash painted on the tail someplace. The rest of the aircraft is grey or green colored. You might be right though.

Going by probability it's likely a KC-130 as there are quite a few of those in the world. The recognition feature would be that it has four teardrop pieces of underwing gear with the external fuel tanks inboard and the drogue refuelling systems on the outboard.  There are no other obvious lumps or bumps in the picture to indicate other mission equipment such as cameras or weapons systems to narrow down which particular variant it could be.

It could also be an AF HC-130.  The USCG also has HC-130s, but their white and orange paint job would indicate this is not a USCG aircraft..

Looks like It's Lockheed C130 Hercules, but don't know which variant it is.

it's got either extra-range fuel tanks or weapons systems installed...

@nielsnielsen The only armed C-130's are the AC-130 gunships, and this is clearly not a gunship.

@Davidw There are other C-130 variants with weapons systems on them such as the KC-130J of the USMC which can, in certain fits, carry hellfire missiles and drop small-diameter bombs.          https://m.youtube.com/watch?v=hIodcKSIARU

It's it's either KC-130E/H, MC-130P, HC-130P/N, all of which are In-flight Refueling capable as this C130 is due to the outboard Refueling pods on either wing, the items inboard of those are the external fuel tanks (which every variant has) both are hard mounted and fixed and can't be air dropped as some like to think. Without a more detailed photo along with a more of side profile exact model and variant can't be known. Try looking up which branch either Navy/Marines, Coast Guard (since paint scheme can't be identified either), or Air Force operates C-130s and you should get an answer. It's more then likely one of the first 2 branches mentioned more probably the first one given the location you stated and will wind up being a KC-130 operates by either Navy or the Marine Corps


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How do commercial pilots send distress signals?
If a commercial jet is in trouble, how does a pilot send a signal indicating distress? Does it take long?
For instance, behind reception desks in many institutions and executive offices, there's a hidden red button that, when pressed, calls security or the police. (I know this since I sit at such a desk.) Do commercial airliners have a similar switch, or do they need to radio in for help? What happens when such a transmission is received?

There are three common ways to send a distress signal (roughly in order of preference):

Over the radio, to whoever you are currently talking to.
Key the microphone and announce to the world Mayday, Mayday, Mayday, the flight's callsign, and a description of the emergency. This is generally the way an emergency is declared, particularly for commercial (airline) service, as they're generally always in contact with an ATC facility
Over the radio, to anyone monitoring the "emergency" frequency.
The VHF frequency 121.5MHz is reserved for aircraft emergency communication. It is monitored at most air traffic control facilities, as well as by many airliners and other pilots with multiple radios in their aircraft. If you're not able to make contact with the facility you're currently talking to in (1) above (or if you're not currently talking to an ATC facility).
Using the aircraft's transponder.
Three transponder codes are reserved for unusual/emergency situations:
7700 for general emergencies
7600 for loss of communication (radio failure)
7500 for hijacking or other unlawful interference
All of these transponder codes alter the way the aircraft's radar target is displayed, to alert the controller to the possible problem (exactly how the display is modified depends on the radar equipment the controller has, and can range from additional text in the data block, like RDOF (RaDiO Failure) for code 7600 to changing the color of the displayed block on newer systems.
Bret detailed some of the procedures around these codes in his answer, and more information is available from the FAA, though you'll have to dig through a few referenced documents to put it all together.

Note that sometimes the order of preference changes - For example if a pilot is being threatened by a hijacker they may quietly set their transponder code to 7500 without saying anything on the radio to alert the hijacker.

A nice mnenonic for the transponder codes: seven five, man with knife; seven six, radio to fix; seven seven, going to heaven.

The transponder is only effective within radar range, right? How does that compare with the range of the radios?

@DavidRicherby Radar coverage depends on where you are - for example on some oceanic routes you're likely to be out of radar range, but still in radio contact with someone (either the oceanic controllers or other aircraft). If you're using any of these transponder codes you're likely to be heading back toward an airport though, and once you're in radar range the code will be detected and handled appropriately.

If you're already in contact with a controlling agency, you aren't required to say Mayday, its much simpler, and often much less chaotic (since everyone cringes when they hear mayday) to simply say "Callsign xxx declaring an emergency".  Plus you'll also sound like a huge dork if you go full on mayday after having just said something to center 30 seconds ago.

What about pan pan.

@CGCampbell There is a subtle distinction between "Mayday" and "Pan-Pan": A mayday call indicates distress: (there is imminent danger and if we don't do something right now people will die) , while pan-pan indicates urgency (a problem that does not yet pose an imminent danger to safety of flight or people's lives). In US aviation it's a distinction without a difference as both calls get you priority handling and assistance, though technically a mayday (distress) has priority over a pan (urgency).

@voretaq7 You might want to expand your answer by adding the ELT technology.

Also note that you can be given emergency status by ATC at their discretion, if they feel that the flight is threatened.

@voretaq7 A very nice example of Pan-Pan-Pan is Quantas 32 Heavy. The pilot chose this signal to warn the ATC so that the ATC can prioritize whatever the plane in trouble may need. Indeed, they needed a lot of airspace for a wide turn and the longest runway on the airport very soon :)

It depends on the type of distress, but generally the easiest way to communicate a problem is to use the radio and describe the situation. However, there are some special transponder codes which will get the attention of any controller which has you on their radar screen.

7500 indicates a hijacking
7600 indicates a communications radio failure
7700 indicates an emergency

What happens after switching to one of these beacon codes depends on the scenario. In any of the cases, ATC will attempt to make contact with the aircraft. In most cases, they will also try to vector other traffic away from the aircraft for everyone's safety (especially true in the case of a hijacking).
I assume your question is primarily asking about a hijacking scenario. A recent, and very odd, example of 7500 being used is Ethiopian Airlines’ Flight 702 where the co-pilot actually hijacked the plane and squawked 7500. Unfortunately, pilots don't always have the time to reset the transponder if they are engaged in a physical fight in the cockpit. Also, the first step of the hijackers may be to turn off the transponder (this is what happened on 9/11), but if a controller is able to see the 7500 squawk, even briefly, it may help the controller understand what is happening if communications are lost, and to alert the military, if necessary.
As for the other two "distress" signals:
For 7600 (lost communications) they will probably ask "if you're receiving this, ident" or "if able, reset transponder code XXXX." If you comply with their request, it indicates that you can receive messages, but cannot transmit. A tracon or center controller might ask you to ident to acknowledge further instructions (when you ident, your datablock flashes on their screen), or just watch your actions closely. If you're on with a tower controller in visual conditions, rocking your wings or flashing your landing light can be used to acknowledge instructions. At towered airports, light-gun signals are used to give landing clearances when a pilot cannot receive radio communication.
For 7700 (emergency) they will try to inquire as to the state of the emergency and offer any assistance possible, such as providing you suggested headings or information about nearby airports.

And what do you do when multiple situations apply?  Say, a hijacker smashes your co-pilot's head into the radio -- do you squawk 7500 for the hijacker, 7600 for the smashed radio, or 7700 for the co-pilot's head injury?

You generally opt for the most severe issue.

There is another procedure which has not been mentioned although I doubt it's ever been used.
If you are lost and the radio has failed and the transponder has failed, flying at least 2 triangles is a recognised distress signal.
Since the transponder has failed, this does require that someone sees you on primary radar which is a long shot.

Do you have a source for that? It's certainly not anything I learned getting a PPL-ASEL.

@bartonjs It wasn't taught as part of my PPL either.  I think it's one of those things  that still exists but is so rarely used, no-one teaches it and it's not on the formal syllabus.  This question contains the details and references.

One incident that I heard (listening to ATC recordings) was a case where a pilot was suffering from hypoxia (lack of oxygen).
In this case, there was nothing wrong with the aircraft, but the pilot itself was incapacitated; so he could not initiate the normal procedures to declare an emergency.
He repeatedly keyed the mic, and then (in slurred speech) tried to communicate. The ATC controller couldn't pick it up but luckily another pilot understood the situation and related to ATC.
I will try to find the transcript for the recording. The ATC recording is available on YouTube.

so where is that transcript?

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text:
Does a vortex/wake turbulence reach ground level nearby?
Where I live not many houses are built under the immediate approach/takeoff line of airports. Instead, they use the area for, say, sports fields.
Is it possible, in otherwise no-wind conditions, for a vortex/wake turbulence caused by a landing/taking-off aeroplane to dislodge a cricket bail on a nearby sports field? How close would the sports field have to be to the runway for this to possibly happen?
In the case at hand the (horizontal) distance is about 1.5 km and the plane (737?) was landing (directly overhead) some time before.

From personal experience (used to run through an area near the approach end of a runway), I can say that they do reach the ground, but are not very strong.  Don't have any experience of cricket balls, though :-(

According to the FAA vortices from the very largest planes generally do not drop vertically below 1000ft of the flight path. So, large aircraft flying less than 1000ft (300 meters) overhead have the potential of being felt on the ground.
This YouTube video shows a fatal aircraft accident after a medium sized prop airplane flew about 100ft above, and 40secs before the takeoff of a small plane.

The FAA addresses vortex generation and avoidance in AC_90-23G.pdf and the following information encompasses some of that information. In general, pilots are told to be weary of vortexes for 5min, 5mi, and 1000ft below. The following diagram supports this generalized rule...

Flight tests have shown that at higher altitude the vortices from large  aircraft sink at a rate of several hundred feet per minute (upto 300 fpm), slowing their descent and diminishing in strength with time and distance behind the wake-generating aircraft.
6 things determining vortex strength and behavior
1) Aircraft Speed - As the velocity of an aircraft increases, the strength of the vortices is typically reduced. That's because flying faster typically requires a lower angle-of-attack. It's also why takeoff and landing are critical times to pay attention to the flight path of large aircraft around you, because they're going relatively slow and creating large vortices.
2) Aircraft Weight - The heavier the aircraft, the more lift must be produced to sustain flight. Increased lift also increases vortex strength. The A380 below is a great example of this.
3) Angle of Attack - Higher angles of attack result in stronger vortices. You have a stronger difference between low and high pressure around the wing with a high angle of attack.
4) Wing Configuration - Clean configurations result in stronger vortices, because higher angles of attack are typically needed.
5) Proximity to Ground - When your wing is close the ground, wingtip vortices can't get as big, because as they spin around your wingtip, they impact the ground and dissipate. This is a major part of ground effect.
6) Wind - While wind doesn't change the strength of vortices produced, it does impact the way vortices affect you. Wind speed and direction determines how vortices travel and dissipate. For instance, if you have a strong crosswind, the vortices produced by airplanes will float in the direction of the wind.

The aircraft was likely flying near 250-275ft altitude
most approaches are 3deg
1.5km=4920ft
.0524 = tan(3deg)
height(ft) = dist(ft) * tan(deg)
257(ft) = 4920ft(dist) * .0524 (tan(3deg))

"unless the aircraft are flying less than 1000ft" well, given the data in the question, as John K says, it would have been at about 300ft.

The 737 would have passed over only about 3-400 ft overhead.  The vortices move downward and apart, and without wind and turbulence to disrupt them they spin for quite a long time, a minute or two, although they tend to break up into segments.
On a windless day where there is actually a wind but it's only a knot or two, the vortice on the upwind side, with a wind speed = to the vortice's lateral drift rate, may end up descending straight down to the ground.
If the wicket stumps are loosely installed where a sharp blast of wind could move them around enough to make the bail fall off, that could be possible.  Or, someone kicked it...

Thanks. About that kicking. The video evidence shows that no person (or their bat) touched the wicket. But I should say that the video is inconclusive about the ball itself (frame rate simply too low). Yet nobody (umpires, wicket-keeper, batsman) noticed/heard/saw.

The wicket bears some resemblance to very early seismometers -- maybe a tiny earthquake?


text:
Seatbelt safety and quick release
Seatbelts, are said to be the object that causes the most deaths in emergency situations on airplanes. (this part is hearsay, just ancillary! :) )
I free-dive, and one of the rules we were taught is that for emergency situations, the diving belt should be set up so that it is released with your preferred hand. So, unclip opening from left to right for a right-hander, and vice verse for a left-hander. (the belt buckles are the same)
This is a rule to stop confusion and save time in emergency situations, for obvious reasons.
My observation is that, given that 90% of the world is right handed, it would make sense to make all of the seatbelts right-hand quick release, but as I see them, on every airline I have flown, the seatbelts are 50/50, and randomly dispersed.
Seems like a very cheap miss to increase safety in emergency situations!
[question] are there no free divers who design airplanes?!

What exactly is your question about seatbelts?

Then you're going to have left handers launching civil rights suits over anti-left-hand discrimination.

@John K - if the system is consistent, then left handers can be told to be prepared for the quick release being right handed, having been informed in the safety video!

@IlyaGrushevskiy - Maybe you can add a citation or reference to where it is said that seatbelts contribute to deaths in aviation. Most GA airplanes use seatbelts similar to car seatbelts. Airliner seatbelts are generally one of two designs. Both are fairly ambidextrous. Maybe your anecdotal evidence is from the use of racing or military  style safety harnesses. Helicopters and airplanes that fly with their doors/canopies open or removed, and aerobatic airplanes sometimes use a style nicknamed the dial-o-death due to it being complicated to use for a novice.

Aviation seatbelts generally are no more difficult to operate than automotive seatbelts. Safety harnesses are the exception in both industries. Both have left-hand and right-hand seatbelts. And, both have fatalities that might have survived if not for the seatbelt. Cars more so than aircraft. Anecdotally, most of those fatalities can be linked back to the inability of the panicked individual to operate their seatbelt regardless of their dominant hand-seatbelt orientation. Some are linked to jammed seatbelts. Making all seatbelts right-handed would not fix this.

If you look closely, you will notice that you can unclip the seatbelt assembly from the seat. If one is worried whether they are able to unclip the seatbelt in an emergency, they can switch the "handedness" of the buckle.
To be honest, if this buckle thing was actually noticed to be a factor in injury rates, something would definitely have been done already. Aviation is a very very very safety oriented industry (exluding certain Big plane manufacturers recent major slip), and you can rest assured, that a simple issue like this would have been fixed if it actually was an issue.

Are you saying that an airline passenger can unclip the seatbelt assembly from the seat and then clip it onto on the other side without tools?

Yes. They are not permanently bolted on. At least on any acft I've ever flown on, and I've flown on many.


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How calculated the drag coefficient lift coefficient with pressure coefficient?
I have got the Cp Plot on a wing, now  I am trying to calculate Cl and Cd. And the angle of attack is 0 degrees, the wing has been split into N Panels, and the normal vector ni for every Panel is already known, The airfoil(AQUILA) is like the picture:

If the friction can be ignored.
For Cl, I integrate Cp with x from 0 to 1;
For Cd, I integrate Cp with y from 0 to breadth of the airfoil.
I have tried several ways:

(CD, CL) = sum(Cp(i) * L(i)* n(i))/(reference length)

-Here L(i) is the length of the i 'th panel, Cp(i) ist the pressure of center point of the i 'th panel and n(i) is the normal vector for the i 'th panel.

like the below equation in the screenshots:

With these two methods, I can get the same Answer, Cl = 0.09, Cd = 0.006
But actually Cl should be 0.2~0.4.
Could someone give me some advice and explain, I haven't studied aerodynamics before, but there are a few parts about that in my paper

did you integrate the pressure on both sides?

Yes, I have integrated every panel length, from point (1,0) to (1,0). Do you think  I have lost something? Thanks for your reply!

It seems you added all pressure coefficients for all panels, multiplied by the panel's length. Now I wonder whether you forgot to normalize the result by dividing by the reference length. Your first equation indicates as much and the result of the summation is a length, not a dimensionless value. So it needs to be divided by a reference length.

Yes, you are right, I have forgotten to add die reference length here, but in my calculation, I have already divided the length, to calculate Cl, the reference length ist the chord(usual 1), and for Cd, the length is breadth in the y-axis.

The reference length should be the same for both coefficients.

Thanks for reminding me! so both length should be chord? but will it  change the answer? cause the chord equal to 1. have I got the correct the understanding?

hey Peter, I have found an explanation about that, but I don't understand why. Cause I have only used source and sink in panel method, and sources and sinks don’t create any drag/lift. but do you know why?

Thank you for asking a new question. That was the right thing to do. Now it should be clear where the error is: Sources and sinks only simulate an obstruction but cannot generate lift. Please read @JZYL's answer – I couldn't explain it any better.

thank you anyways!


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Why are FDR's called "black boxes" when they are actually orange?
Why do they call flight data recorders a "black box" if it's orange in color?

Just curious about this since I've seen several images of black boxes but they all come in orange colors, and not black.  I can understand orange being used to help brightly identify the box , but then why call it a "black" box?

I have always thought of it as a (western) cultural influence. Many people believe these boxes are read only after a fiery crash, i.e. with fatalities. Death is associated with black in western cultures, hence the name.

A black box (generally speaking) is a device or box whose internal working are not of as much interest or value but rather the input and output.
Flight data recorders are orange so that they can be located easily in case of a crash. If they were black, they can be camouflaged by their surroundings.
Bright orange color make them stand out easily, because nature didn't make many things orange, besides oranges.
Another reason is that they are painted/coated with heat-resistant bright orange paint.

+1 for the update.  I suspect that may be the real answer - in electronics it's a common term and from an avionics point of view this is a "don't care" box.  The avionics will work fine without it.

So black doesn't necessarily connotate color but actually conveys the condition of the box?

"Nature didn't make many things orange, besides oranges." Well, apart from various other fruit, lots of flowers, various butterflies, birds, autumn leaves, the sunset, ... (Sunrise, too, I hear but I'm rarely awake then.)

Another possible reason can be"Just like black hole which contains all light this is black box which contain all the necessary flight data". This flight reveal every important information of flight as if whoever decodes it can identify flight trajectory, surface position, engine rpm, warnings etc.

I think this is the correct answer, but the point is not that the internal workings are not of interest, but that apart from the actual data inputs they are totally isolated and separate from the rest of the system so that the do not fail when the rest of the system fails. That lack of dependencies is what makes the internals "not of interest" both for FDR and for "black boxes" in general. And what allows black boxes to serve their function after the rest of the plane has broken to small pieces scattered over several square miles of ocean.

The Wikipedia article on Flight recorder offers a possible explanation for the origin of the term:

... they were essentially photograph-based flight recorders since the record was made on a scrolling photographic film. The latent image was made by a thin ray of light deviated by a mirror tilted according to the magnitude of the data to record (altitude, speed, etc.). Since the inside of the recorder was pitch black, this may be the origin of the "black box" name, often used as a synonym for a flight recorder.

Interestingly, the Wikipedia article on Black box claims that the term entered the English language around 1945, which is a few years after the first flight data recorder was built.

The correct answer seems to be, "Nobody knows for sure" but here's some data.
The earliest citation in the Oxford English Dictionary for the phrase "black box" referring specifically to a flight data recorder isn't until 1964, from the UK Daily Telegraph: "The flight recorder is an indestructible 'black box' which automatically records the key functions in the aircraft..."
There are earlier uses of the phrase, with different meanings. Since 1932, it has been used to mean a device whose internal workings are unclear but which is specified by its inputs and outputs; since 1945, it has been used in the Royal Air Force to refer to various navigational devices which, according to Wikipedia sometimes were housed in literal boxes that were black.
My interpretation/thoughts/speculation/whatever word you want to use:
The use of quote marks in the Daily Telegraph seems significant. First, it suggests that we're not talking about a literal box which is black and you might imagine they'd say something like " 'black box' (which is now actually orange)" if they were formally literal black boxes. Second, "a 'black box' " suggests that the FDR might be just one of several devices on a plane that could be described as "black boxes". Unfortunately, that seems consistent with both of the other given definitions: you could perfectly well imagine it being RAF-style slang for "This electronic box of tricks does navigation, this one holds the autopilot and this one records flight data" or the input-output version of "I don't know exactly how the autopilot works, but I know what it does; ditto the navigation system; ditto the data recorder."

The adjective "black" in "black box" means "opaque".  Engineering also uses the phrase "black box testing", which means tests that are done without access to system internals.
Similarly, "white box" means transparent, in which internal signals may be recorded or manipulated.
A black box recorder is presumably recording pilot actions on the system as well as the state shown to the pilot on the instruments, but none of the avionics internal variables.  I doubt any modern FDR would be designed this way, however, since without the internal variables diagnosis of failure could be very difficult.

Actually, I think it's the recorder that is a "black box", rather than the signals being recorded. You don't know how it records the data. You don't normally care how it records the data. In fact you normally don't know or care what data it records. As far as the pilot is concerned, it's just a mysterious piece of avionics which gets tested periodically, gets ignored most of the time, and hopefully will never actually be used.

When you say that a black box recorder "presumably" does certain things and that you "doubt" that one would do other things, it suggests rather strongly that you're speculating. It also sounds like you're not quite sure what a black box does.

@David: This question asks about terminology, I don't think one needs to know about every model of FDR in use.  Do you mean to imply that there aren't variations between FDRs in use in different aircraft, different fleets, different countries?  (Of course the pilot conversations, actions, and displayed data are recorded, but these are only the minimum data set)  I'm not trying to provide the ultimate authoritative answer here, just provide additional context which I feel believe to be helpful.

@keshlam: That's a good point, although I would say it's not that pilots don't care, but that the recorder functions best when it is opaque and cannot be manipulated by the crew.

Also a good point. Tamper resistance is a Good Thing if you want to catch and critique the "oops" moments as well as the outright disasters.

Since the Flight Data Recorder measures aviation inputs and outputs, it could be construed as “black-box testing” the plane itself. So maybe the term originally identified what it does, not what it is.

One other theory I've heard (but been unable to verify) about the origin of the term "black box" in popular literature is that the boxes when found often tend to be black.
Not as a result of being painted black, but as a result of having been inside a burning aircraft wreck, covered in soot and burnt paint.

Whether that's the (or even one of the) reason for the term is probably lost in the mists of time. I seriously doubt it's ever been written down by the people inventing the term (newspaper journalists most likely) what their reasoning was.

The black box was invented by Professor Gordon Black at Farnborough in 1948 - hence the name 'black' box. See Who really invented the black box?

Well at least my source makes a lot of sense rather than a lot of the assumptions above that are based on nothing more than someone's personal view

It's good that yours is a factual claim, it makes it either completely true or completely false.  Your claim is completely false, as black boxes were being used in Finland as early as 1942 (see Wikipedia for details, which are sourced to a museum possessing physical evidence from 1946, two years before the supposed "invention").


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How does British Airways permit a 23 kg bag in hand baggage?
The carry-on baggage policy on British Airways states that:

Maximum weight per bag is up to 23 kg (51lbs).

Two passengers, with bags near the weight limit could easily go well over 40 kg. And then there will be a few smaller laptop bags etc. inevitably stuffed into the overhead compartment, I imagine it can touch 50 kg.
However, the overhead compartments themselves have a stated limit of 32 kg. Isn't this an unsafe practice? If so, how is British Airways permitted to do so, and if not, why do other airlines not follow the same practice?

under seat storage

A bag like http://safari.in/store/media/catalog/product/cache/1/image/950x/9df78eab33525d08d6e5fb8d27136e95/1/_/1_1.jpg can easily carry 20KG, and 2 of these fit overhead. They cannot fit in the under seat storage and will tough 40KG even if everyone keeps laptops,etc under the seat (which they dont)

I see the aviation (safety) aspect here, but the answer could be a purely business one, e.g. BA has estimated (or gathered data) to show that customers never carry such heavy bags anyway but by 'allowing' it they can make the statement on the same page for Marketing purposes that "We offer one of the most generous free hand baggage allowances of any airline". If you don't get a good answer here you may want to try travel.stackexchange.com instead because I think there's a large business practice component to it.

@Akash: The bag can carry 20kg in a sense that it won't break with such load. But you won't find that many things with sufficient density to actually weight 20kg, fit in and make sense to take on a trip.

This decision does appear to be a marketing strategy. Most airlines allow two check-in bags when flying over Atlantic. Hence BA wants to entice people by allowing heavier bags. Obviously not everyone will stuff a small bag with 23kg.

Where did you read that the overhead bins have a limit of 32kg? This seems low.

@JanHudec I've frequently packed ~15KG into those when checking them in,primarily clothes and I'm not the most efficient packer :)

@DannyBeckett There were stickers indicating them in the compartments, didnt take a pic though. Example: http://airwaysnews.com/galleries/american-airlines-boeing-777-300er-inaugural-main-cabin-20_26130.jpg

even if they say 32kg, they are probably designed for some multiple of that

Using the same logic phone companies can serve a 1000 house neighborhood with a junction switch that can only handle 100 calls: the average per customer is far lower than the allowed. In marketing/sales this is called "overselling" (or oversubscribing).

You can fit a lot more than 32 kg in most overhead bins

Easyjet has no firm weight limit and advertises this fact. From the website

There’s no weight restriction for cabin baggage, as long as you can place and retrieve the cabin bag safely in the overhead lockers without assistance.

They also use vague language like “within reason” or “lift comfortably” but most people probably won't have 20 kg with them. Given the limited size of cabin luggage, you would need to deliberately carry dense, heavy stuff to reach that weight (books maybe? wine bottles and other liquids are off-limits and if you don't want to check in any bag you still need space for your other things).
And then, comes this (from the BA website you mentioned):

Occasionally we may not have space to stow all hand baggage safely on board and you may be asked to check in some or all of your hand baggage at the boarding gate.

Bottom line: Airlines don't need to rely on a prespecified weight limit at all. They rely on the size restrictions and general common sense to keep things manageable and if it somehow does not work out, they can always gate check a few bags.

Looks like it isnt really a safety issue at all..

I'm curious about the "without assistance".  Some people do need assistance, even for lighter weights many would fine easy to handle.  My wife, for example, broke her elbow awhile back and now (after recovery) can't use that arm to lift things. (In practice she's always easily been able to find help from a fellow passenger.)

FWIW, Most U.S. airlines also impose no weight limit on carry-on baggage, as long as it complies with the standard dimensions. Most U.S. airlines don't weigh carry-on bags at all.

@reirab Interesting. Most European airlines that do place a limit on carry-on weight according to their terms and conditions don't actually weigh carry-on bags either, not sure why they still pretend to have restrictions like that.


text:
What kind of WWII aircaft is this?
I saw this plane at a warbird fly in and would appreciate some assistance identifying it.
I can only tell you what I'm rather sure it's not..
Grumman TBF Avenger

Other US-operated Torpedo Bomber types

Grumman F4F-3 Wildcat

Republic P-47 Thunderbolt
Any ideas?

[EDIT]
Also, is this yellow aircraft the same model, only with a different paint scheme? The nose looks different, but perhaps the cap/cone has been removed, perhaps for maintenance. Otherwise the canopy, wheels, and gear covers look identical.

A North American T-6 Texan Trainer, probably the NJ/SNJ Texan variant.

"SNJ-1 at NAS Pensacola c1940" by U.S. Navy - U.S. Navy National Museum of Naval Aviation photo No. 1996.488.166.090. Licensed under Public Domain via Commons.
The North American Aviation T-6 Texan is a single-engined advanced trainer aircraft used to train pilots of various air forces including (but not limited to) USAAF, USN, RAF from (before) WWII well into the 1970s.

Thanks, @aeroalias. Please see my edit--is the yellow aircraft I added also a T-6 Texan? It looks very similar and I nearly created a separate question for it, but after reading your wiki link (noting they are common at air shows), I'm wondering if it is indeed the same model aircraft.

@elrobis http://www.aerialvisuals.ca/AirframeDossier.php?Serial=66332

Ahh gotcha: "Markings Applied: TA-533, 12533, 77". Thanks CG!

Note that without verifying the serial number we can't know for sure but I'd hazard that the airplane in the link I gave you and your photo #2 are one and the same bird.

Where did you spot these? Do. They appear to be based there?


text:
Can anyone identify this 1910s era biplane?

I tried a number of searches with absolutely no luck. I remember a few that looked sort of similar without that smooth aerodynamic nose and body. I did try at least.
If this helps, the individual standing before the plane is believed to be of French origin or descent.

Interesting. It doesn't look like it's a fighter, as there's no armament visible, although it could be something in development. As a two-bay biplane with an inline engine, it's at least a little unusual.

Sturtevant made aircraft with similar features (http://ivanpwheaton.blogspot.com/2012/02/grover-loening-and-sturtevant.html) although I don't see an exact match for this aircraft yet.

My first guess would be an early Curtiss model.

The Halberstadt family, predecessor of the Albatros has also some similarities.

Two makes that immediately came to mind on seeing the picture were Pfalz and Albatross. Most "Albatri" had trapezoidal wings instead of square, though, and most Pfalz D.IIIs which would have had the aerodynamic shape were known for a much larger engine protrusion from the top of the fuselage (and a much lower top wing).
I'm not sure about the French origin of the plane; French (and British) biplanes of the era typically used radial engines, with the Se.5 being a notable exception (and the SE5 wasn't nearly so aerodynamic-looking).
My best guess is, maybe, a DFW C.V:

These were WWI reconnaissance aircraft that came in several different engine configurations as the war progressed. Austria's Aviatik firm made some of these as the C.VI, as well as some very similar designs like the C.1, C.II and C.III. Here's a picture of the C.III; body is similar but the lower wing is shorter:

The radiator in front of the top wing on the C.V is a little larger here than in your picture, but it's possible, even probable, that the radiator configuration also varied (could be as simple as a 90* rotation). Wing shape and strut configuration are very similar. Your picture may have been a "war prize" delivered to the French after the Armistice, and de-militarized (disarmed, markings removed) for civilian use.
Here's another C.V that looks a little more like yours but without the nose cone, but this makes it look like a much bigger plane than is depicted in your shot:

The amount of cutout varies from picture to picture; these planes weren't built fully assembly-line style like modern fighters. Engines, props, even tail configurations varied significantly between batches or between factories making them, especially toward the end of the war when the Germans were low on supplies and were piecing planes together more or less from spare parts.

KeithS, I have accepted your answer because it's at least interesting and useful but I have a competing claim to the identity of this mystery plane from elsewhere: Pitcairn PA-3 Orowing. What do you have to say about it?

In the right engine configuration, sure. The wings definitely match; I haven't seen a PA-3 with a cutout. However I've only seen one other picture with the engine shown in yours, and that one didn't have a nose cone on the prop: http://www.aerofiles.com/pit-pa3.jpg It would be nice if there were at least one other shot from a different angle, allowing us a look at the fuselage and tail; that would really pin it down.

There's also the matter of the pushrod that connects the upper and lower aileron in this picture http://www.aerofiles.com/pit-pa3.jpg. That is not present in the aircraft that is being identified in this question.

It isn't German or even European, not with an OX-5 engine on the front - unfortunately there were hundreds of similar designs in the post-ww1 period, however the fact that it has a two bay wing and the struts are wire braced instead of having a diagonal narrows it down, and lo and behold, the Pitcairn PA-3 Orowing appears to be a match.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. - From Review

@mins Yes, it does. It doesn't get much clearer than "the Pitcairn PA-3 Orowing appears to be a match."

Mike and @DanHulme: I agree, it's a valid answer. My bad, sorry for that. +1.


text:
How do large airliners de-ice in flight?
How do large airliners de-ice their surfaces in midair? In smaller planes like the ATR or the caravan there are deicing boots as per picture:

How is this achieved on bigger aircraft, as there seems to be no such mechanism?

I once asked a 787 pilot. He said they don't do anything because the compression/friction of air heats the wings enough. I felt skeptical but went with it. Seeing other answers, I decided to google for it, and sure enough, 787 has heating elements inside the wings. Weird for a 787 pilot not to know?

Hot bleed air is drawn from the engines and directed through control valves and ducting to the leading edges of the wings and stabilizers.
This is what it looks like on a 727. Note that the upper VHF antenna is also anti-iced to prevent ice entering the engine inlets.

The 787 uses electric heating elements for the wing instead of bleed air from the engines. Engine anti-ice is still done using engine bleed air.

Putting this as an answer rather than a comment because of its length.
In response to @romkyns comment, perhaps the 787 pilot knew of the heating elements within the wing but was simply telling how ice was normally handled. I really can't imagine him getting through his type rating oral without knowing that.
Had you asked me the same question back when I was flying 747-100 and -200 aircraft, I would have replied thus:
Icing isn't typically a problem because you're usually not in it long enough at a slow enough speed that the ram air temperature rise doesn't get the temperature above freezing.
If you are getting ice on climb out at your normal climb speed, it was usual to ignore it knowing that the icing would soon stop as you gained altitude, and then what icing you had would soon sublimate. If the icing was severe enough to warrant your attention, the usual remedy was to just speed up to get more ram air temperature rise, but you would, of course, be sacrificing some of your climb rate. The U.S. has a 250kt speed limit below 10,000 feet, but you don't have to (or at least didn't have to back then) observe that if there was an operational need to go faster, and generating enough heat to take care of icing was considered a good reason. You normally wouldn't have to think about that though because a 747 climbing out with flaps up has a minimum safe airspeed in excess of 250 anyway.
One indication that the icing was serious was that ice buildup on the windshield wipers would set them to vibrating and giving off a loud buzzing sound. If you let them do that too long, they could depart the aircraft. As I understood it, the time for that to happen was cumulative over the past occurrences as well as the current occurrence, as it was a matter of fatigue.
If you were icing on the approach and didn't want to or couldn't speed up, you could heat the wing leading edge with pneumatic air as described in previous answers. However, it was the leading edge slats that were heated, and when you selected the first notch of flaps, that deployed the leading edge slats, and the heated pneumatic air escaped with little or no effect.
Only once in 10 years of 747 flying did I use the leading edge heating. We were in a holding pattern at low altitude waiting for our turn for an approach into Brussels.

Apart from pumping hot air, there are a few ways to achieve wing's leading edge de-icing. Most reliable is through electric heaters just beneath the wing surface.
Other are more tricky.
One solution is an elastic leading edge, which can be pushed out by, for example, a linear hydraulic motor. If the ice thickness is just right, it will crumble and fall off. If it is too thin, it will deflect beyond the reach of the mechanism, and of course if it is too thick then nothing can be done.
Other wings adapt a series of small holes in a leading edge surface, through which a liquid can be pumped, called a "weeping wing" or TKS.
I heard there also are mechanisms which adapted vibrations, but I can give no source on this one right now.

Those are both used on smaller airplanes, but I've not heard of a "large airliner" -- as per the question -- that uses either of these methods.

authors: علی گنج خانلو


text:
How do engine manufacturers minimize damage from bird strikes?
What are the ways that engine manufacturers currently minimize the damage caused to engines in a bird strike?

That is one idea proposed by someone and more importantly Not in Use, and the answers to that question too try to find the feasibility of the suggested idea. My question pertains to measures already in use. Please consider. Thanx

@Simon Agreed with OP: this is not a duplicate of that question, because this is about the current state of the art.

It has been discussed here http://aviation.stackexchange.com/questions/3450/how-are-jet-engines-certified-against-birdstrikes

See: Aircraft Certification for Bird Strike Risk. Also on Wikipedia: Bird strike | 3.1 Vehicle design

Some pilots were not too happy with certification standards in 2000: "The ability of modern jet engines to ingest birds and continue to operate is largely misunderstood or not contemplated at all in the aviation industry. Currently there is not one jet engine operating in the world that is certified to ingest one large bird (goose, swan, stork, pelican, vulture, etc) and continue to operate". US Air Line Pilots Association. I hope that changed...

The vulnerable moments are take-offs and landings. The question is how airports, and not engine designers, minimize birds being sucked into jet engines. There is a handful of means here to keep birds far from the runway.

@mins That's not really very surprising. At 250-300 mph, a 10 lb. bird is a pretty good approximation of a cannon round. Small birds usually get chopped up easily enough by the intake fan, but a large, dense one is a (literally) much bigger problem.

@reirab: I agree. The article tackles the limited coverage of current certification vs actual threats.

Placement on aircraft that fly above birds. This is the #1 reason we don't hear about airliner bird strikes every day on the news; cruise altitude for airliners is around 30,000 feet, while only two species of bird have ever been recorded flying at that height, one in Central Africa, the other around the Himalayas, neither of these being common travel lanes for airliners. The critical time for most bird strikes is below the cloud ceiling and/or transition altitude, above which the air becomes thinner and birds have to work harder to stay aloft. Thus most birds fly below transition, while airliners spend as much of their flight time as feasible above it as the thinner air reduces drag and lowers fuel consumption (the "strata" of thicker air at the transition point, in addition to the simple reduction of SPL on the square of distance, also helps insulate people on the ground from jet noise).
Strong intake fan fins. The first set of turbine fins that you see looking into a nacelle are the ones in the direct line of fire. They're also the largest fins, but in their favor there are higher acceptable tolerances for those fins versus the ones in the compressor stages. So, they're built strong to hopefully survive ingesting your average goose. Here's a YouTube of the A380 engine's bird strike test; the engine continues to operate even though the blade that was struck is misaligned on the turbine hub for a few rotations.
Garbage disposer effect. At ascent throttle levels, an airliner's engines are rotating between 10,000 and 15,000 RPM. Even travelling at cruising speeds of 500-550 knots, the rotation speed of the turbine will chop most organic matter into mincemeat in a fraction of a second. In fact, bird strike tests show the bird carcasses literally exploding from the force of impact with the rotating blades. These smaller pieces cause fewer problems passing through the engine.
High bypass. About 80% of the air volume entering most underwing airliner engine nacelles passes around the turbine chamber instead of through it, increasing thrust while reducing fuel consumption. Fuselage-mounted engines on older aircraft had lower bypass ratios (one of the reasons those designs are being phased out of modern fleets). A bird entering the engine has a similar chance to pass right on through without encountering the combustion chamber.
Reinforced nacelle housing. In the event a bird strike does dislodge something in the engine, the nacelle housing is engineered specifically to contain the shrapnel, minimizing the chance of damage to fuel and control lines in the wings and of course to the fuselage. (Here's a YouTube of a "blade-out test" for the A380's Rolls-Royce engines) The pilots will be alerted the engine has failed, and will cut off the fuel supply, engage fire suppression and run on the remaining engine(s).
Overspecification of required engine thrust. One of the major tests an airliner design must pass before being FAA certified is an "engine cutout at decision" test. An aircraft is loaded to MTOW, taxis to the runway, the engines are spun up, the aircraft rolls out, then at the "decision speed" above which the pilot must commit to a takeoff, an engine is idled. The aircraft must still be able to get off the runway and attain a minimum climb rate. That test, for most modern two-engine jets, shows that the plane is perfectly capable of flying on one engine (if such a thing happened at takeoff in real life the jet would circle and land again but it would not have to risk an aborted takeoff above decision speed).

In short, these engines are built tough and tested tough, as is the rest of the aircraft (manufacturers build several planes' worth of components and subsystems for the express purpose of torture testing, and that's if they get it all right the first time). In addition to bird strikes, engines are tested for water ingestion, hail strikes, sand ingestion, smoke ingestion (a British Airways 747 lost all four engines after flying through the upper ejecta cloud of an erupting volcano; they got two restarted and landed safely, but future engine tests got even more stringent to avoid a repeat performance), and a host of other things that just aren't good for jet engines.
The most famous bird strike incident in recent memory, Sully Sullenberger's emergency water landing in the Hudson River, was caused by hitting not one or two, but an entire flock of birds, and not sparrows or pigeons, but Canada geese, which can weigh up to 20 pounds each. This incident is still a good example of how well engineered these engines are; both engines would have been at full revs as the plane was climbing out of LaGuardia, yet AFAIK the turbines, though deformed, didn't even part company with the hub, saving the control surfaces and lines for the ditch attempt, resulting in no fatalities and only one hospitalization.

"and the engine can operate at least for a little while with a fan blade broken or even missing." Do you have a source for this?! That would require some serious vibration tolerances. I'd be very surprised if an off-balance 11-foot-diameter fan with tips flying around at Mach 1.3 ended well. It should contain the thrown blade within the cowling, as you said, but continuing to operate is another matter entirely.

I overstated things; the engine is not expected to survive a blade break but the turbine hub and remaining blades are expected not to disintegrate completely. Here's a YouTube of the Blade-Out test for the A380's engine: https://www.youtube.com/watch?v=j973645y5AA

Ah, yeah, I was aware of that requirement. My internship during undergrad was actually at a USAF jet engine/rocket motor/wind tunnel testing facility. They had just completed testing the Trent 900s when I got there, IIRC. However "not disintegrating catastrophically" is a quite different requirement from "continuing to operate." The engine won't blow up, but you'll likely be replacing the entire engine after such an event.

Also, I would point out that airliner bird strikes actually do happen pretty much every day. It's just that most of them are small birds that get chopped up into fine particulate matter by the main intake fan, as you mentioned. They do sometimes need to send the engine to maintenance afterwards, though. One of the flights I was on a few weeks ago had to change planes right before boarding because the pilots found evidence that it had ingested a bird during its previous flight during their preflight checks.

I once was a part of a presentation where they showed the research results about the fan blade breaking and still the engine surviving. @reirab

@VictorJuliet Define 'surviving.' Not disintegrating or having an uncontained failure? Sure. Able to continue operation while missing a blade? Almost certainly not. Able to pop in a new blade and continue operation? Almost certainly not. Able to replace lots of broken/deformed parts and get the engine working again? Maybe. You might be lucky enough to have the core come out relatively undamaged, since the thrown blade will generally travel around the inside surface of the nacelle (i.e. away from the core,) but the vibrations and likely stall aren't going to be good for the core.

@reirab The project was regarding containing the vibrations in limits so that the engine could operate. That is based on the assumption that the broken fragments do not cause further problems after being ingested.


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How do airliner manufacturers come up with typical capacities of their planes?
Instead of providing the maximum capacity of a particular model, airliner manufacturers often provide official typical capacities, like 280-366 seats for A350 series and 350/400seats for Boeing 777x series.
The question is: How do they generate this number?

These numbers are based on mixed-class configurations and use of floor space for other things. The A380 for instance can theoretically be configured with 853 "economy" seats, but no-one I know of has bought one configured that way. Typical first-business-economy configuration is 525, and Emirates seats just 489 because its first-class section is basically staterooms, and it has showers and a bar taking up floor space (it also has an excellent and large business class instead of using the back half of both decks for coach).
When designing an aircraft's seating capacity, especially for long-haul flights, total cabin weight (passengers and cargo) must be taken into account. The more stuff you're hauling, the less weight allowance you have for fuel, and therefore your range is reduced. Therefore, increased room per passenger on long-haul flights isn't just for passenger comfort, it's often a necessity to reduce total cabin weight and thus be able to max out the fuel load to get between the airports non-stop. Operators of shorter flights don't care as much because you can pack them in like sardines and still have plenty of fuel to get them where they're going.
Therefore, dimensions of various classes of seat differ by airline, aircraft and route (Lufthansa, for instance, operates three different A380 configurations based on the routes they run). The typical coach seat is between 17 and 19 inches wide (including half the armrest), and has a "pitch" (space between seats which determines the legroom and ability to recline) of between 31 and 35 inches.
For business class in three-class planes it gets a bit better; seat width averages about 21" and a pitch of about 38" (more for planes outfitted with lay-flat seats). First class ranges widely by aircraft type and airline (it's truly "first-class" in aircraft with three-class configuration; in two-class what's called "first" is closer to business class), but typically offers room to spare especially on long-hauls.
Coupled with required/desired aisle widths and additional amenities that widen the seats or replace them in certain areas of the cabin, it's fairly academic to count up how many seats you can fit aboard a particular airframe.

I don't think most airliners have their passenger capacities limited by weight.  As I commented on another answer, the Boeing 777-300ER has a maximum payload of about 400,000 pounds or more, assuming fuel for a long flight.  That's the weight of roughly 2,000 people - but nobody would say the plane has a capacity of 2,000 passengers, or anywhere near that number.  The evacuation time mentioned by user6396 has a major effect on how tightly the seats can be packed.

Fair point, it's a bigger deal for the jumbos. The A380 can carry over 800 passengers, but doing so with full fuel as well will exceed MTOW, and as the economics of a jumbo typically only make sense for long-haul, nobody's bothered ordering an all-economy A380.

The FAA average passenger weight (adult male) is 200 LBS in the summer and 205LBS in the winter, you can extrapolate seats from that number. It is assumed that there is one passenger to a seat. You would also need to assume that the worst case is a plane full of adult winter males (205LBS) plus luggage. The document linked goes over how to calculate average baggage weights and what some rough percentages are on that.
It should be noted that people who are above standard size may be required to buy 2 seats. This is generally handled on a case by case basis it seams.

It seems unlikely that these capacities are produced purely based on weight.  For instance the Boeing 777-300ER has a maximum payload of roughly 400,000 pounds for a long flight - but it would be absurd to say it has a capacity of 2,000 passengers.

authors: محمد صادق سیروسی


text:
Gyroscopic Precession in Coaxial Helicopters
I'm trying to understand gyroscopic Precession in the case of coaxial helicopters. Obviously the effect still exists. But if gyroscopic Precession is a result of counter torque. Shouldn't the effect be canceled out in a coaxial helicopter?


text:
What is an Air Defense Identification Zone (ADIZ)?
China recently caused some controversy by announcing an Air Defense Identification Zone (ADIZ) in the East China Sea. There is also an ADIZ surrounding most of North America.
What exactly is an ADIZ and what does it take to fly across one? For example, what would be necessary to fly a private plane directly from Apalachicola to Cedar Key, Florida?

What is an ADIZ?
FAR 99.3 says:

Air defense identification zone (ADIZ) means an area of airspace over land or water in which the ready identification, location, and control of all aircraft (except for Department of Defense and law enforcement aircraft) is required in the interest of national security.

To put it simply, if you're going to fly in the United States ADIZ, the United States government wants to know:

Who you are
Where you are
What you're doing

What do I need to have before I fly through one?
A few things, actually.  They're listed in AIM 5-6-1

You generally need to file a flight plan (but there are exceptions). (FAR 99.11)
You need a two-way radio. (FAR 99.9(a))
You need to have a Mode C transponder, and it has to be on. (FAR 99.13)
If you're going DVFR (rather than IFR), you need to give an estimated time of ADIZ penetration at least 15 minutes before entering it. (FAR 99.15, also reference AIM 5-6-1.4b)

What do I need to do while I'm in one?

Remain no more than 5 minutes off the proposed ETA to your various waypoints
Remain no more than:

10 miles from the centerline of your route, if over land
20 miles from the centerline of your route, if over water


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How is pressure related to air density?
This is confusing to me:
Since pressure increases with temperature (I don't know why), how can air density decrease with temperature. In a hot day then pressure would increase and air density decrease? How is that possible?

@casey @steve V. @StallSpin
The point is this: FAA writtten says:
The altimeter will indicate lower altitude than actually flown in a temp warmer than standard. I understand that this way: this an example
1) Indicated Altitude: 12.000ft
   True Altitude: 12.000ft
   Temperature: -9 Celsius (STD)
Then suddenly the air temperature changes from -9 to +20 (Example) and in a couple of minutes we have:
Indicated Altitude: 12.000ft
   True Altitude: 14.000ft
   (In warmer than stantard, pressure increases so the aneroid waffers in the altimeter will contract indicating lower altitude (lets say it indicated 10.000), then the pilot will climb "back" to 12.000 but in reality (true altitude) he is climbing to 14.000.
Am I getting this right?
2) Now another thing, temperature decreases with altitude, so aneroid waffers are expanded with altitude.
Does the aneroid waffers mesure density or pressure?

Pressure will increase with temperature in a closed environment. If you seal air in a container and heat it the pressure will go up. The atmosphere is not a sealed container, when you heat air it will expand as it is seeking equilibrium. When air expands it decreases in pressure.

You might also be correlating that with altitude changes, where both the temperature and pressure lowers, which isn't necessarily the case in other situations.

@GdD if you heat a parcel of air it will initially have the same pressure as its surroundings but its density will decrease.  This parcel with reduced density is now buoyant and will rise, and as it rises it will expand and cool adiabatically as it seeks equilibrium and cease rising when it is no longer buoyant.  The parcel expands because of decreasing atmospheric pressure with height (not the other way around).

The atmosphere approximates an ideal gas, and as such you can relate pressure and density through the ideal gas equation.  The form we use in meteorology uses mass density and is given by:
$$p={\rho}RT$$
where $P$ is pressure in units of Pa, $\rho$ is density in units of kg m-3, $R$ is the gas constant for dry air (287 J kg-1 K-1) and $T$ is temperature in Kelvin.  This assumes a dry atmosphere and humidity will decrease density for a given pressure.  Consideration for water vapor is usually brought in by changing temperature into virtual temperature $T_V$ where $T_V=T(1+0.61q)$ and $q$ is the mixing ratio of water vapor (units $kg~ kg^{-1}$).

Pressure increases with temperature because the particles have more kinetic energy (which is proportional to $T$).  Imagine a box full of bouncing balls, if these balls start moving faster the balls will hit the walls of the box harder, imparting more force on the box.  Pressure is merely force per area, so if the force increases but the box stays the same size, the pressure has increased.

Air density can decrease with temperature if pressure is also decreasing.  If pressure is constant, this cannot happen (they would be inversely related).  Any time you specify a relation between any two of pressure, density or temperature you must hold the third constant or specify its behavior.
For example, hot air rises, but why then is it cold on top of a mountain.  The answer is that hot air is less dense than the cold air surrounding it for a constant pressure, and being less dense it rises.  With a mountain, the pressure is decreasing, and we likewise find in the atmosphere that temperature decreases with decreasing pressure.

On a hot day what tends to happen is that the surface, which is being warmed by the sun, heats the lowest level of the atmosphere, reducing its density (it is at the same pressure as its surroundings and its T rises).  This will eventually drive convection and mix this warmer air vertically.  Given enough time, this will reduce the mass in the column of air and therefore reduce the pressure at the surface.  These are called "heat lows" and you can see them forming in the desert areas and they play roles in sea breeze formation and the monsoons.

To address the expanded question:
The point in the FAA written is best understood by forgetting that we fly at constant altitudes -- we don't.  In level flight we fly on constant pressure surfaces which we then translate to an altitude.  In any given column of atmosphere, if it is warmer than standard a given pressure surface will be higher and when colder than standard the pressure surface will be lower.
To illustrate, let's consider you are flying at 3000 ft or roughly 900 mb.  Everywhere on this pressure surface will indicate 3000 ft on our altimeter for its current setting.  If we go somewhere hot, this pressure surface rises, and so we climb (though we think we are level) with this pressure surface but because the pressure has not changed, we still indicate 3000 ft.  However, we are higher than 3000 ft in reality.
This follows into your next question.  Aneroid wafers detect pressure changes and your altimeter displays an altitude not corrected for temperature.  This is why your true altitude can vary with temperature for a constant indicated altitude.  When you correct the altitude for temperature we call this "density altitude".
So back to my example above, your are flying along at 900 mb and indicating 3000 ft, and heading into warmer air.  The pressure surface starts to gently rise and as it does you are not yet following that rise and your altimeter will indicate a descent.  In true level flight you will begin to fly into higher pressure in this case as the 900 mb surface rises above you and the aneroid wafer in your altimeter will indicate a lower altitude and a descent.  You correct this and climb back up to the 900 mb pressure level so that your altimeter will once again indicate 3000', all the while actually gently climbing on this pressure surface.  You won't really be cognizant of this while flying however, and will just minimize vertical speed and maintain altitude blissfully unaware that you are really flying on a sloping constant pressure surface.
To better illustrate this, consider the following figure:

In this figure the reds signify a warmer than average column of air and the blues a cooler then average column.  The whitish area in the middle is a column at average temperatures.  The black solid lines are isobars (lines of constant pressure).  The dashed black line is a true altitude above the surface. Finally, the bold black line is the pressure level that corresponds to the true altitude of the dashed line at ISA conditions.
What you should notice is that the pressure levels in the warm column are spaced further apart because the air is less dense and more of it is needed to produce the same pressure (as pressure is just the weight of all the air above it).  Likewise in the cool column the pressure levels are spaced closer together because the air is more dense than standard.
To tie this into the discussions above, consider yourself in the standard column (white background) at the true altitude above ground represented by the dashed line.  Your altimeter does not sense this true altitude but instead senses the pressure outside of the airplane.  This will be roughly calibrated to your true altitude (uncorrected for temperature) but using the local altimeter setting.  Now as you fly either to the left or to the right and maintain a constant indicated altitude, you will track along the bold line, as this is the pressure that corresponds to your true altitude at standard temps.  As you fly toward a colder column you will in reality descend, and you will climb as you fly into the warmer column.

Thank you. Very interesting.
One last question:
Does pressure affect airplanes performance (temp increase pressure increases)?

Aircraft performance is greatly affected by air pressure, measured by density altitude. The higher the density altitude (the lower the pressure) the less performance you get. It can make an enormous difference which is why you should always do your performance calculations as part of your pre-flight.

It is important to state, that when it's hot, the pressure surfaces will be further apart and when it's cold they will be closer together. Because the pressure is caused by weight of the air above and it takes thicker layer of less dense warmer air to have the same weight. The insidious outcome is that you set the altimeter to match true altitude at ground level, but higher it will still differ due to the temperature.

Oh, and density altitude is a density.

Now Im confused: Pressure increases with temp.
Aircraft performance is affected by pressure.             Aircraft performance decrease in warmer than standard.
How can an aircraft have a greter performance with a lower pressure?

@camilogv Density is what you are really after, not pressure.  You can only say something like "Pressure increases with temp" if you qualify what is happening to density (as discussed in my answer).  It is a problem of 3 variables, not only 2.  Consider that if I heat a parcel of air, this is a constant pressure problem and density will decrease.  Also consider that as you climb higher into the atmosphere, which is no longer a constant pressure problem, density is decreasing (as is temp).

@JanHudec I've added a bit to my answer to include your comments and an attempt to illustrate it with a figure.

@casey "If we go somewhere hot, this pressure surface rises"
This is where I get lost. Isn't hotter air lower pressure out in the open? Shouldn't the pressure surface sink? Air in a hotter area is less dense and lower pressure, no? So to find the same pressure, you have to descend, thus being pulled down by hot air (via the altimeter). What am I missing?

A big thing to remember is that $Density=\frac{Mass}{Volume}$. It is unrelated to pressure, and pressure is unrelated to density.
Pressure generally increases with temperature only in a gas with a constant volume. This is because you are adding more energy to the system, causing the molecules to become more exited. To put simply, they bounce around harder and exert more energy on each other and the walls of their container. We call that pressure.
If there were no container, an increase in temperature would cause the molecules to fly apart. Now there are less molecules per unit of volume, so the density is lower.
Now in aviation and meteorology when we talk about atmospheric pressure, that is slightly different, and is less related to atmospheric density. High and low pressure systems are more affected by relative upward and downward motion of huge air masses than by immediate local temperature, as a contained gas would be.

Pressure, density and temperature are related (approximately) through the ideal gas equation. In the general form it is
$$PV=nRT$$
Where $P$ is pressure, $V$ is volume, $n$ is amount, $T$ is temperature and $R$ is ideal gas constant. If you have an enclosed container filled with air, volume ($V$) and amount ($n$) are the same, so pressure increases proportionally to temperature.
In free atmosphere, however, the pressure is determined by the weight of the air above and thus mostly fixed, so by heating the air it increases volume instead.
To get to density, we divide the equation by volume and arrive at:
$$P=\rho RT$$
Where $\rho$ is the density (and handwave the switch from amount to mass, hiding the gas-specific conversion factor in the gas constant). The outside pressure is constant, so the density actually decreases as temperature increases.
Practical effect of this is that since engine power depends on amount of air it can draw in the fixed volume of the cylinders performance is worse when it's warmer.
Now it remains to be explained what governs the open air pressure. The pressure at any given point is caused by the weight of the air above it. Because from the above at constant temperature the density is proportional to pressure, the full equation is differential.
$$\Delta P \sim \rho\Delta h$$
In words the change of pressure is equal to difference in height times density.
The pressure at ground level is affected by weather systems in complex ways. But since colder air is denser, it means that when it's cold the pressure will decrease faster with altitude than when it's hot. Now the altimeter really measures pressure and it only has adjustment for sea-level pressure, but not for temperature. So when you set your altimeter on the ground and climb 1000 feet, you'll be more than 1000 feet above ground when it's hot because the pressure decreases slowly and less than 1000 feet above ground when it's cold. Some procedures even have minimal temperature because of this.


text:
What is the cockpit shown in this picture?
What is the cockpit shown in the picture below?

Is the bottom picture relevant? If not, can it be cut-out?

There are two...

Judging by the way the shadows appear on the 'windows' I'd say this isn't a real cockpit at all, but a simulator.

The cockpit shown in the photo is of a Boeing 747-400.
You can tell that it must be a 747 by the fact that it has 4 thrust levers (so 4 engines) in the typical Boeing design. The 6 screens with the EFIS controllers rule out anything older than the 747-400 (like a B707 or older B747 variants). The large gear lever with the 3 positions rules out the new 747-8 variant.
Here is a cockpit picture for comparison:

(image source: Wikimedia)

In addition, it has yokes instead of side sticks, making it a Boeing instead of an Airbus.

The top picture looks like it may be in a simulator, rather than an actual aircraft. Based on the screen around the windows.  Though if an actual jet had fabric around the outside of the flightdeck windows... can't say for certain.

@SnakeDoc The Airbus A300 and A310 have yokes as well. But no Airbus quad-jet has yokes, they all have sidesticks.

@Bianfable Exactly. So the presence of yokes narrows down the make to a Boeing, furthering the conclusion.


text:
Privately owned charter planes or jets flight naming conventions
Do privately owned charter planes and jets require a mandatory three digit or four digit flight number with a flight naming convention similar to Commercial airlines carriers following IATA or ICAO rules and regulations?
Do the above naming rules & regulations apply to Private Owned Helicopters?
If yes, what are the flight naming conventions?
If no, what are the reasons?

Source

Thank you. Can you specify private jet charter planes call signs for "India" with examples?

"privately owned charter planes & Jets", is nor very clear, your question seems more about "how are charter flights from small operators numbered in India compared to scheduled flights from large operators having a 2- or 3-letter ICAO operator identifier".

At least at the airports I'm familiar with, private jets (and at least some charters) don't use the passenger terminal at all.  At my home airport, they're mostly at FBOs on the opposide of the field.

A "call sign" is a business' name plus the (typically) three or four digit flight number.
In all ICAO member countries, private pilots use the airplane's registration number when communicating with ATC. There isn't a flight number, nor is there a company name, so the plane's registration number is all that's available to identify the flight.
Similarly, the big commercial carriers always use call signs. The "business name" is typically registered with the government, but the numbers themselves are assigned by the airline in whatever system they want to use. Usually, the only rule is that you can't have two planes with the same call sign in same airspace simultaneously (although some countries do have stricter rules than that).
For charters, small commuter airlines, etc., there is a lot of variation between countries, so I can't get more specific without knowing which country you're asking about. For instance, the FAA allows any corporation that's registered as an airline and certain charity organizations to request to be allowed to use call signs, but it's not required; they can continue to use airplane registration numbers if they so choose.

Thank you. Can you provide some examples to illustrate "Call Signs"?

@PrashantAkerkar it could basically be anything, as long as it's approved by aviation authorities and doesn't conflict with other operators. That's also why such things aren't that common on international flights as the approval would have to be obtained from all countries where the aircraft enters their ATC zones.

@Prashant here is an example or three

@PrashantAkerkar If you want a quick example, British Airways is a pretty distinctive and ubiquitous one - there you hear ATC referring to BA flights by the callsign "Speedbird".

@J: A call sign is not the same as a flight number, and 'speedbird' will be used only on voice exchanges, not for air traffic management systems. "British Airways flight 238 would display [...] BA238 on passengers’ boarding cards[...]. To the air traffic controllers it appears as BAW29G and when the controllers and pilots communicate via radio, you would hear ‘Speedbird Two Niner Golf ’" (more). See Call sign Confusion

The (very fuzzy) screenshot in your question only shows IATA 2-letter/digit airline codes. Those are only used in airline booking systems, so they are only assigned to airlines. This code is followed by a flight number (assigned by the operator) of one to four digits.
ATC uses 3-letter ICAO codes and associated callsign, and those are available to any operator that does the paperwork and pays the fees. This code is followed by a flight number (assigned by the operator) that is up to four numbers and letters. This often matches the IATA flight number, if any, but this is not required.
For a list of ICAO codes/callsigns and what companies they belong to, see FAA JO 7340.2K, Section 3. Note: the final letter of that changes over time as the document is updated.
Operators who don’t have an approved code/callsign must use the tail number of each plane.

Thanks. Do the above naming rules & regulations apply to Private Owned Helicopters?

@PrashantAkerkar They apply to all aircraft.